Means for controlling augmentor liner coolant flow pressure in a mixed flow, variable cycle gas turbine engine

ABSTRACT

The present invention discloses means and method for modulating the bypass flow in a mixed flow, variable cycle gas turbine engine. The engine includes means to vary the bypass flow and includes an augmentor and liner with coolant supplied by a portion of the bypass flow. The bypass flow pressure is modulated by sensing the pressure of the liner coolant and the pressure in the augmentor and varying the flow pressure as a function of P 1 , P 2 , or both.

This is a division, of application Ser. No. 057,642, filed Jun. 8, 1987(U.S. Pat. No. 4,813,229), which is a continuation of Ser. No. 708,181,filed Mar. 4, 1985 now (abandoned).

This invention relates generally to augmented gas turbine engines and,more particularly, to a method for controlling augmentor liner coolantflow pressure.

BACKGROUND OF THE INVENTION

Gas turbine engines generally comprise a compressor for compressing airflowing through the engine, a combustor in which fuel is mixed with thecompressed air and ignited to form a high energy gas stream, and aturbine for driving the compressor. One type of gas turbine engine foran aircraft is the turojet in which thrust is provided by the highvelocity gas stream exiting the turbine.

A second type of aircraft gas turbine engine is the turbofan in which afan is mounted forward of the compressor and is driven by a secondturbine or power turbine mounted downstream of the first turbine. Thefan produces a flow of pressurized air which is split into two portions.The first portion enters an outer bypass duct for bypassing the coreengine and the second portion enters the compressor of the core engine.One advantage of the turbofan engine over the turbojet is its ability tomove a larger mass of air and thereby increase the thrust output of theengine.

Another feature which may be utilized to increase the thrust output of agas turbine engine is an augmentor. In an augmented gas turbine engine,an exhaust duct is provided downstream of the turbine(s). Additionalfuel is injected into the exhaust duct and is ignited to increase theenergy of the gas stream. The gas stream is ejected through an exhaustnozzle to increase the thrust output of the engine.

One type of engine which combines features of the turbofan and augmentedengine is a mixed-flow engine where fan airflow is mixed with the coreengine gas stream after the turbine but forward of the augmentor. Acharacteristic of turbofan engines, especially high bypass turbofanengines, is relatively low specific fuel consumption at subsonic speeds.A characteristic of turbojet and relatively low bypass turbofan enginesis relatively high specific thrust characteristics at supersonic speeds.

In order to satisfy the need for aircraft which must efficiently operateover a wide range of subsonic and supersonic speeds, so-called variablecycle engines have been developed. Such variable cycle engines arecharacterized by the capacity to change the bypass ratio of the engineduring operation. For example, U.S. Pat. Nos. 4,010,608 -Simmons and4,175,384 -Wagenknecht et al disclose variable cycle engines. Eachvariable cycle engine disclosed includes an outer bypass duct and avariable area bypass injector for modulating the flow through the bypassduct thereby varying the engine cycle.

The augmentor in such variable cycle engines is normally located withinthe exhaust duct from the engine. In order to protect the exhaust ductfrom the extremely high temperatures associated with the gas flow withinthe augmentor, a cooling liner may be positioned within the duct so asto form a cooling plenum therebetween. A portion of the bypass flow maythen be diverted into this plenum for cooling of the same.

A fundamental problem in the design of an augmentor liner is thepressure differential that may exist between the coolant flow within theplenum and the gas flow inside the liner. The problem becomesparticularly acute when the pressure inside the liner suddenly drops.For example, a sudden decrease in the fuel flow to the combustor(throttle chop) will slow the core engine down and reduce the pressurewithin the augmentor faster than the pressure of the bypass air.Therefore, the design of the liner must provide some means forpreventing the inward collapse of the liner.

In the past, various techniques have been proposed to overcome thisproblem. For example, adequate support such as hangers or couplings maybe provided to retain the liner within the duct. However, such solutionsadd additional complexity and weight and increase the manufacturing costof the liner. Another means of control is disclosed in U.S. Pat. No.3,866,417, Velegol, wherein the plenum is divided into a number ofindividual chambers with flow into each chamber being regulated byflanges which restrict the airflow and regulate the pressure. Thissystem is effective but requires extra structural members to achieve theresult. Another solution to the problem is disclosed in U.S. Pat. No.4,072,008, Kenworthy et al, in which a valve is used to regulate airflowto the augmentor liner. Kenworthy et al discloses an effective means forregulating pressure in the plenum. However, both Velegol and Kenworthyet al require some additional structure to the liner system whichresults in an increase in cost.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a new and improvedmethod of controlling augmentor liner coolant flow pressure in a gasturbine engine.

It is another object of the present invention to provide an inexpensiveand lightweight means for controlling augmentor liner coolant flowpressure in a gas turbine engine.

SUMMARY OF THE INVENTION

One form of the present invention is a method for modulating the bypassflow pressure in a mixed flow, variable cycle gas turbine engine. Theengine is the type having a bypass flow and means to vary the bypassflow pressure, and having an augmentor and liner with coolant suppliedby a portion of the bypass flow. The method comprises the steps ofsensing the pressure P₁ of the coolant and the pressure P₂ in theaugmentor, and varying the bypass flow pressure as a function of P₁, P₂,or both.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic, cross-sectional view of a mixed flow,variable cycle gas turbine engine incorporating the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The FIGURE shows a mixed flow, variable cycle gas turbine engine 10.Engine 10 has a core engine 12 which includes a compressor 14 forcompressing air flowing therethrough, a combustor 16 where fuel is mixedwith the air to form a high energy gas stream, and a turbine 18 whichextracts energy from the gas stream for driving compressor 14. Coreengine 12 generates a gas flow 20.

Engine 10 further includes a front fan 22 driven by a second turbine 24located aft of first turbine 18. Fan 22 is located within an inlet 26and is effective for pressurizing air 28 entering inlet 26. An aft fan30 is located downstream of front fan 22. Aft fan 30 is driven byturbine 18. However, it will be clear that the invention is not limitedto this configuration and may be driven by second turbine 24 or thirdturbine (not shown). Aft fan 30 further pressurizes air flowingtherethrough.

A bypass duct 40 directs bypass flow 42 around core engine 12. Bypassduct 40 includes a first bypass duct inlet 32 which directs a firstairflow 34 around aft fan 30. A second bypass duct inlet 36 directs asecond airflow 38 from aft fan 30 into bypass duct 40. In this manner,second airflow 38 is mixed with first airflow 34 thereby forming abypass flow 42.

Varying means for varying the bypass flow pressure in bypass duct 40 areshown at 44 and 46. According to one form of the present invention, thevarying means includes a diverter valve at 46 such as disclosed in U.S.Pat. No. 4,068,471 -Simmons. According to another form of the invention,the varying means may include a variable area bypass injector includinga double-bypass selector valve at 44 and a static pressure valve at 46such as disclosed in U.S. Pat. No. 4,175,384 -Wagenknecht et al.According to yet another form of the invention, the varying means mayfurther include a variable area bypass injector at 47 (a rear VABI)which effectively reduces the area of bypass duct 40.

Other varying means will occur to those skilled in the art and arewithin the scope of the present invention. The characteristics of suchvarying means are that first bypass duct inlet 32 and second bypass ductinlet 36 may be fully open creating a turbofan mode of operation, andfirst bypass duct inlet 32 or second bypass duct inlet 36 may be fullyclosed while the other is fully open creating a lower bypass turbofanmode approaching a pure turbojet cycle. Furthermore, the varying meansmay be capable of being positioned in an intermediate position to allowfor a bypass flow 42 made up of flows 34 and 38. Accordingly, a featureof the present invention is that the areas of first bypass duct inlet 32and second bypass duct inlet 36 may be changed. A further feature of thevarying means is that the valve at 46 may be configured so that byvarying the area of second bypass duct inlet 36 an abrupt change in thecross-sectional area of second bypass duct inlet 36 will be created forairflow 38 passing therethrough. In this manner, a pressure dump loss orpressure drop will occur for airflow 38 passing therethrough. In theevent that a rear VABI is used, it may be opened as airflow 38 undergoesa dump loss so that the pressure of bypass flow is reduced while themass flow remains generally constant.

Located aft of core engine 12 is an augmentor 48 surrounded by anexhaust duct 50. A cooling liner 52 is positioned within duct 50 so asto form a cooling plenum 54 therebetween. Receiving means 56 forreceiving a portion 58 of bypass flow 42 into plenum 54 is located atthe forward end of liner 52. Mixing means 60 for mixing bypass flow 42with gas flow 20 is located aft of core engine 12 and forward ofaugmentor 48. According to one form of the present invention, the mixeris of the variable geometry type as disclosed in U.S. Pat. No. 4,069,661-D. J. Rundell et al.

First sensing means 62 senses the pressure P₁ in plenum 54. For example,sensing means 62 may be a pressure transducer or other means well-knownin the art. Similarly, second sensing means 64 senses the pressure P₂ inthe augmentor 48. A control system 66 will receive pressure signals P₁and P₂ and send a signal to the varying means to actuate valve at 46and/or 44. If P₁ exceeds P₂ by a predetermined value, the valve at 46may be moved towards a closed position. In this manner, airflow 38 fromsecond bypass duct inlet 36 to bypass duct 40 will undergo a pressuredrop. This pressure drop will reduce P₁ relative to P₂ thereby reducingthe radially inwardly directed forces on liner 52.

It is also possible to develop a control system which monitors only P₁or P₂. For example, control system 66 could respond to maximum values ofP₁ or sudden changes in the value of P₂. It should be clear that controlsystem 66 may also control the valve at 44 or the valves at both 44 and46 in order to achieve control of pressure P₁ through modulation of thebypass flow pressure in bypass duct 40.

Another feature of the present invention is that the dump loss createdin the forward bypass duct may result in performance improvement. Grossthrust is the product of mass flow and the flow velocity. In enginessuch as shown in the figure, airflow is limited by a maximum mach numberthrough mixer 60. The dump loss created by valve 46 results in adecrease of total pressure of bypass flow 42. Since total pressure is afunction of mach number, this also reduces mach number through mixer 60.Accordingly, the speed of engine 10 may be raised thereby increasing themach number of the bypass flow through mixer 60. The higher speed ofengine 10 increases mass flow through the engine thereby increasingthrust.

It will be clear to those skilled in the art that the present inventionis not limited to the specific embodiments described and illustratedherein. Rather, it applies equally to any variable cycle engine withmeans to vary the bypass flow in that engine.

It will be understood that the dimensions and proportional andstructural relationships shown in the drawing are by way of exampleonly, and these illustrations are not to be taken as the actualdimensions or proportional structural relationships used in the variablecycle engine of the present invention.

Numerous modifications, variations, and full and partial equivalents cannow be undertaken without departing from the invention as limited onlyby the spirit and scope of the appended claims.

What is desired to be secured by Letters Patent of the United States isthe following; what is claimed is:
 1. A gas turbine engine comprising:acore engine for generating a gas flow; a front fan for pressurizing air;an aft fan for further pressurizing air discharged from the front fan; abypass duct including a first bypass duct inlet which directs a firstbypass airflow around the aft fan into said bypass duct, a second bypassduct inlet which directs a second bypass airflow from the aft fan intosaid bypass duct; an augmentor aft of said core engine; an exhaust ductsurrounding said augmentor; a cooling liner positioned within saidexhaust duct so as to form a cooling plenum therebetween; means forreceiving a portion of said bypass flow into said plenum; means formixing said bypass flow with said gas flow; a first sensing means forsensing a control pressure in said exhaust duct; and a varying means formodulating the flow pressure in said bypass duct as a function of atleast said control pressure.
 2. A gas turbine engine, as recited inclaim 1, wherein said varying means includes means for changing the areaof said second bypass duct inlet and means for changing the area of saidfirst bypass duct inlet.
 3. A gas turbine engine, as recited in claim 2,wherein said varying means includes means for changing the area of saidbypass duct.
 4. A gas turbine engine, as recited in claim 1, whereinsaid varying means includes means for creating a pressure dump loss insaid second bypass duct inlet.
 5. A gas turbine engine, as recited inclaim 1, wherein said control pressure is a first control pressure P₁ insaid plenum.
 6. A gas turbine engine, as recited in claim 1, whereinsaid control pressure is a second control pressure P₂ in said augmentor.7. A gas turbine engine, as recited in claim 5, further comprising:asecond sensing means for sensing a second control pressure P₂ in saidaugmentor; and wherein said function is a function of said first controlpressure P₁ and said second control pressure P₂.
 8. A gas turbineengine, as recited in claim 2, wherein said control pressure is a firstcontrol pressure P₁ in said plenum.
 9. A gas turbine engine, as recitedin claim 2, wherein said control pressure is a second control pressureP₂ in said augmentor.
 10. A gas turbine engine, as recited in claim 8,further comprising:a second sensing means for sensing a second controlpressure P₂ in said augmentor.
 11. A gas turbine engine, as recited inclaim 3, wherein said control pressure is a first control pressure P₁ insaid plenum.
 12. A gas turbine engine, as recited in claim 3, whereinsaid control pressure is a second control pressure P₂ in said augmentor.13. A gas turbine engine, as recited in claim 11, further comprising:asecond sensing means for sensing a second control pressure P₂ in saidaugmentor; and wherein said function is a function of said first controlpressure P₁, and said second control pressure P₂.
 14. A gas turbineengine, as recited in claim 4, wherein said control pressure is a firstcontrol pressure P₁ in said plenum.
 15. A gas turbine engine, as recitedin claim 4, wherein said control pressure is a second control pressureP₂ in said augmentor.
 16. A gas turbine engine, as recited in claim 14,further comprising:a second sensing means for sensing a second controlpressure P₂ in said augmentor; and wherein said function is a functionof said first control pressure P₁ and said second control pressure P₂.